Screed Calculator
Screed is a thin cement and sand layer over a concrete base (or compatible substrate) to produce a smooth, level surface before tiles, resilient flooring, or other finishes. This tool estimates screed volume and dry materials from floor dimensions, thickness, and mix ratio.
Structural slab: concrete slab calculator. General pour volume: concrete calculator. Masonry mortar: mortar calculator.
Screed layer
Volume = area (length × width) × thickness. Typical layers are often ~25–75 mm depending on spec.
Default bulk densities: cement 1440 kg/m³, sand 1600 kg/m³ (override below if needed).
Volumes
Floor area 0.00 m²
Screed volume (placed) 0.00 m³
Dry batching volume 0.00 m³
Materials
Cement (bulk) 0.00 m³ → 0.00 t · Bags: 0
Sand (bulk) 0.00 m³ → 0.00 t
Add roughly 5–10% extra for wastage when ordering.
How this calculator works
Steps:
- Area = length × width
- Screed volume (placed) = area × thickness = length × width × thickness
- Dry batching volume = screed volume × 1.33 when enabled (adjustment from placed volume to dry sand and cement)
- Cement : sand by dry volume: each material = dry batching volume × (its part ÷ sum of parts)
- Mass from bulk densities (defaults cement 1440 kg/m³, sand 1600 kg/m³), plus cement bags from your bag size
Standard screed mix ratios
Typical site mixes (dry materials before water):
- 1 : 3 — higher-strength screed
- 1 : 4 — standard floor screed
- 1 : 5 — light-duty applications
Stronger mixes use more cement for the same dry batching volume.
Where screed is used
- Floor leveling before tiles or sheet goods
- Finishing a concrete surface to line and level
- Patio and outdoor flooring (where specification allows)
- Bathroom and kitchen floors (with suitable damp-proofing and falls)
- Subfloor preparation
Screed is usually not structural like a structural slab, but it strongly affects flatness and performance of the finished floor.
Example calculation
Floor:
- Length 5 m, width 4 m, screed thickness 50 mm (0.05 m)
Step 1 — Area = 5 × 4 = 20 m²
Step 2 — Volume = 20 × 0.05 = 1.0 m³
Step 3 — Dry volume = 1.0 × 1.33 = 1.33 m³
For a 1 : 4 mix (total parts 5):
- Cement ≈ 1.33 × (1/5) ≈ 0.27 m³ — about 390 kg at 1440 kg/m³ — roughly 8 × 50 kg bags
- Sand ≈ 1.33 × (4/5) ≈ 1.06 m³
Enter 5, 4, and 50 mm with ratio 1 : 4 to match.
Importance of thickness
Planning bands (always confirm with your spec):
- ~25 mm — thin leveling where allowed
- ~50 mm — common “standard” thickness in many guides
- 75–100 mm — heavier-duty or special build-ups
Thicker screed increases material cost and dead load on the structure.
Common mistakes to avoid
- Ignoring the dry volume factor — underestimates cement and sand orders.
- Wrong thickness — too thin risks cracking; too thick wastes material and load.
- Wrong mix ratio — weak screed can fail under traffic or deflection.
- Poor preparation — bonding and durability suffer if the base is dusty, oily, or out of tolerance.
Practical tips
- Measure thickness at several points—flatness varies.
- Add 5–10% extra material for wastage.
- Cure properly to limit plastic shrinkage cracks.
- Keep batching consistent across the pour.
Underfloor heating and falls
Slopes to drains and thicker zones over heating pipes change the average thickness. Split the floor into zones or measure average thickness if ordering must be tight.
Frequently asked questions
What is the difference between screed and concrete?
Concrete (in the usual structural sense) includes coarse aggregate and is designed for load-bearing performance. Screed here is a cement–sand layer for leveling and finishing—it is not a replacement for a designed structural slab.
How thick should screed be?
Many flooring specs land around 40–75 mm for typical sand–cement screeds, but underfloor heating, falls, and product systems change the number. Use your drawing or manufacturer data.
Can screed be used outdoors?
Yes, where the specification allows—think patios and external falls. Manage weather during placement and curing (sun, wind, frost, rain).
How long does screed take to dry?
Initial hardening is often on the order of 24–48 hours before light traffic on many traditional mixes, but full drying for sensitive floor coverings can take weeks, especially for thick layers. Always follow project and manufacturer guidance.